4.1. Preparing for the upgrade

We suggest that before upgrading you also read the information in Chapter 5, Issues to be aware of for wheezy. That chapter covers potential issues which are not directly
related to the upgrade process but could still be important to know about
before you begin.

4.1.1. Back up any data or configuration information

Before upgrading your system, it is strongly recommended that you make a full
backup, or at least back up any data or configuration information you can't
afford to lose. The upgrade tools and process are quite reliable, but a
hardware failure in the middle of an upgrade could result in a severely damaged
system.

The main things you'll want to back up are the contents of
/etc, /var/lib/dpkg,
/var/lib/apt/extended_states and the output of
dpkg --get-selections "*" (the quotes are important). If
you use aptitude to manage packages on your system, you
will also want to back up /var/lib/aptitude/pkgstates.

The upgrade process itself does not modify anything in the
/home directory. However, some applications (e.g. parts
of the Mozilla suite, and the GNOME and KDE desktop environments) are known to
overwrite existing user settings with new defaults when a new version of the
application is first started by a user. As a precaution, you may want to make
a backup of the hidden files and directories (“dotfiles”) in users' home
directories. This backup may help to restore or recreate the old settings.
You may also want to inform users about this.

Any package installation operation must be run with superuser privileges, so
either log in as root or use su or sudo to
gain the necessary access rights.

The upgrade has a few preconditions; you should check them before actually
executing the upgrade.

4.1.2. Inform users in advance

It's wise to inform all users in advance of any upgrades you're planning,
although users accessing your system via an ssh connection
should notice little during the upgrade, and should be able to continue
working.

If you wish to take extra precautions, back up or unmount the
/home partition before upgrading.

You will have to do a kernel upgrade when upgrading to wheezy, so a
reboot will be necessary.
Typically, this will be done after the upgrade is finished.

4.1.3. Prepare for downtime on services

There might be services that are offered by the system which are associated with packages
that will be included in the upgrade. If this is the case, please note that,
during the upgrade, these services will be stopped while their associated packages
are being replaced and configured. During this time, these services will not be
available.

The precise downtime for these services will vary depending on the number of
packages being upgraded in the system, and it also includes the time the system
administrator spends answering any configuration questions from package
upgrades. Notice that if the upgrade process is left unattended and
the system requests input during the upgrade there is a high
possibility of services being unavailable[1] for a significant period of time.

If the system being upgraded provides critical services for your users or the
network[2], you can reduce the downtime if
you do a minimal system upgrade, as described in Section 4.4.4, “Minimal system upgrade”, followed by a kernel upgrade and reboot,
and then upgrade the packages associated with your
critical services. Upgrade these packages prior to doing the full upgrade
described in Section 4.4.5, “Upgrading the system”. This way you can ensure that
these critical services are running and available through the full upgrade
process, and their downtime is reduced.

4.1.4. Prepare for recovery

Although Debian tries to ensure that your system stays bootable at all times,
there is always a chance that you may experience problems
rebooting your system after the upgrade. Known potential issues are
documented in this and the next chapters of these Release Notes.

For this reason it makes sense to ensure that you will be able to recover if
your system should fail to reboot or, for remotely managed systems, fail to
bring up networking.

If you are upgrading remotely via an ssh link it is
recommended that you take the necessary precautions to be able to access the
server through a remote serial terminal. There is a chance that, after
upgrading the kernel and rebooting, you will have to fix the system
configuration through a local console. Also, if the system is rebooted
accidentally in the middle of an upgrade there is a chance you will need to
recover using a local console.

The most obvious thing to try first is to reboot with your old kernel.
However, this is not guaranteed to work.

If that fails, you will need an alternative way to boot your system so you can
access and repair it. One option is to use a special rescue image or a Linux
live CD. After booting from that, you should be able to mount your root file
system and chroot into it to investigate and fix the
problem.

Another option we'd like to recommend is to use the rescue
mode of the wheezy Debian Installer. The advantage of using the
installer is that you can choose between its many installation methods to find one
that best suits your situation. For more information, please consult the
section “Recovering a Broken System” in chapter 8 of the Installation
Guide and the Debian Installer FAQ.

4.1.4.1. Debug shell during boot using initrd

The initramfs-tools package includes a debug
shell[3] in the
initrds it generates. If for example the initrd is unable to mount your root
file system, you will be dropped into this debug shell which has basic commands
available to help trace the problem and possibly fix it.

Basic things to check are: presence of correct device files in
/dev; what modules are loaded (cat
/proc/modules); output of dmesg for errors loading
drivers. The output of dmesg will also show what device
files have been assigned to which disks; you should check that against the
output of echo $ROOT to make sure that the root file system
is on the expected device.

If you do manage to fix the problem, typing exit will quit
the debug shell and continue the boot process at the point it failed. Of
course you will also need to fix the underlying problem and regenerate the
initrd so the next boot won't fail again.

4.1.5. Prepare a safe environment for the upgrade

The distribution upgrade should be done either locally from a textmode virtual
console (or a directly connected serial terminal), or remotely via an
ssh link.

In order to gain extra safety margin when upgrading remotely, we suggest that
you run upgrade processes in the virtual console provided by the
screen program, which enables safe reconnection and ensures
the upgrade process is not interrupted even if the remote connection process
fails.

Important

You should not upgrade using telnet,
rlogin, rsh, or from an X
session managed by xdm, gdm
or kdm etc. on the machine you are upgrading.
That is because each of those services may well be terminated
during the upgrade, which can result in an
inaccessible system that is only half-upgraded.
Use of the GNOME application update-manager is
strongly discouraged for upgrades to new releases, as
this tool relies on the desktop session remaining active.

Users of the watchdog daemon provided by the micro-evtd package should stop the daemon and
disable the watchdog timer before the upgrade, to avoid a spurious reboot in
the middle of the upgrade process:

4.2. Checking system status

The upgrade process described in this chapter has been designed for upgrades
from “pure” squeeze systems without third-party packages.
For the greatest reliability of the
upgrade process, you may wish to remove third-party packages from your system
before you begin upgrading.

Direct upgrades from Debian releases older than 6.0 (squeeze)
are not supported.
Please follow the instructions in the Release
Notes for Debian 6.0 to upgrade to 6.0 first.

4.2.1. Review actions pending in package manager

In some cases, the use of apt-get for installing packages
instead of aptitude might make aptitude
consider a package as “unused” and schedule it for removal. In general, you
should make sure the system is fully up-to-date and “clean” before proceeding
with the upgrade.

Because of this you should review if there are any pending actions in the
package manager aptitude. If a package is scheduled for
removal or update in the package manager, it might negatively impact the
upgrade procedure. Note that correcting this is only possible if your
sources.list still points to squeeze
and not to stable or wheezy; see Section A.2, “Checking your sources list”.

To perform this review, launch aptitude in “visual mode” and
press g (“Go”). If it shows any actions, you should review them and either fix
them or implement the suggested actions. If no actions are suggested you will
be presented with a message saying “No packages are scheduled to be installed,
removed, or upgraded”.

4.2.2. Disabling APT pinning

If you have configured APT to install certain packages from a distribution
other than stable (e.g. from testing), you may have to change your APT pinning
configuration (stored in /etc/apt/preferences and /etc/apt/preferences.d/) to allow
the upgrade of packages to the versions in the new stable release. Further
information on APT pinning can be found in apt_preferences(5).

4.2.3. Checking packages status

Regardless of the method used for upgrading, it is recommended that you check
the status of all packages first, and verify that all packages are in an
upgradable state. The following command will show any packages which have a
status of Half-Installed or Failed-Config, and those with any error status.

# dpkg --audit

You could also inspect the state of all packages on your system using
aptitude or with commands such
as

# dpkg -l | pager

or

# dpkg --get-selections "*" > ~/curr-pkgs.txt

It is desirable to remove any holds before upgrading. If any package that is
essential for the upgrade is on hold, the upgrade will fail.

Note that aptitude uses a different method for registering
packages that are on hold than apt-get and
dselect. You can identify packages on hold for
aptitude with

# aptitude search "~ahold"

If you want to check which packages you had on hold for
apt-get, you should use

# dpkg --get-selections | grep 'hold$'

If you changed and recompiled a package locally, and didn't rename it or put an
epoch in the version, you must put it on hold to prevent it from being
upgraded.

4.2.4. The proposed-updates section

If you have listed the proposed-updates section
in your /etc/apt/sources.list file, you
should remove it from that file before attempting to upgrade your
system. This is a precaution to reduce the likelihood of
conflicts.

4.2.5. Unofficial sources and backports

If you have any non-Debian packages on your system, you should be aware that
these may be removed during the upgrade because of conflicting dependencies.
If these packages were installed by adding an extra package archive in your
/etc/apt/sources.list, you should check if that archive
also offers packages compiled for wheezy and change the source line accordingly
at the same time as your source lines for Debian packages.

Some users may have unofficial backported “newer” versions of packages that
are in Debian installed on their squeeze system. Such
packages are most likely to cause problems during an upgrade as they may result
in file conflicts[4].
Section 4.5, “Possible issues during upgrade” has some information on how to deal with file
conflicts if they should occur.

4.3. Preparing sources for APT

Before starting the upgrade you must set up apt's configuration file for package lists,
/etc/apt/sources.list.

apt will consider all packages that can
be found via any “deb” line, and install the package with the
highest version number, giving priority to the first line in the
file (thus where you have multiple mirror locations, you'd typically first name a local
hard disk, then CD-ROMs, and then HTTP/FTP mirrors).

A release can often be referred to both by its codename (e.g.
squeeze, wheezy) and by
its status name (i.e. oldstable, stable,
testing, unstable). Referring to
a release by its codename has the advantage that you will never be surprised by
a new release and for this reason is the approach taken here. It does of
course mean that you will have to watch out for release announcements yourself.
If you use the status name instead, you will just see loads of updates for
packages available as soon as a release has happened.

4.3.1. Adding APT Internet sources

The default configuration is set up for installation from the main Debian Internet
servers, but you may wish to modify /etc/apt/sources.list
to use other mirrors, preferably a mirror that is closest to you in network terms.

Debian HTTP or FTP mirror addresses can be found at http://www.debian.org/distrib/ftplist (look at the “list of Debian
mirrors” section). HTTP mirrors are generally speedier than FTP mirrors.

For example, suppose your closest Debian mirror is
http://mirrors.kernel.org. When inspecting that
mirror with a web browser or FTP program, you will notice that the main
directories are organized like this:

Note that the “dists” is added implicitly, and the arguments
after the release name are used to expand the path into multiple directories.

After adding your new sources, disable the previously existing
“deb” lines in sources.list by placing a
hash sign (#) in front of them.

4.3.3. Adding APT sources from optical media

If you want to use only CDs (or DVDs or Blu-ray Discs),
comment out the existing
“deb” lines in /etc/apt/sources.list by
placing a hash sign (#) in front of them.

Make sure there is a line in /etc/fstab that enables
mounting your CD-ROM drive at the /cdrom mount point (the
exact /cdrom mount point is required for
apt-cdrom). For example, if /dev/scd0
is your CD-ROM drive, /etc/fstab should contain a line
like:

/dev/scd0 /cdrom auto noauto,ro 0 0

Note that there must be no spaces between the words
noauto,ro in the fourth field.

To verify it works, insert a CD and try running

# mount /cdrom # this will mount the CD to the mount point
# ls -alF /cdrom # this should show the CD's root directory
# umount /cdrom # this will unmount the CD

Next, run:

# apt-cdrom add

for each Debian Binary CD-ROM you have, to add the data about each CD to APT's
database.

4.4. Upgrading packages

The recommended way to upgrade from previous Debian releases is to
use the package management tool apt-get. In previous
releases, aptitude was recommended for this purpose, but
recent versions of apt-get provide equivalent
functionality and also have shown to more consistently give the desired
upgrade results.

Don't forget to mount all needed partitions (notably the root and
/usr partitions) read-write, with a command like:

# mount -o remount,rw /mountpoint

Next you should double-check that the APT source entries (in
/etc/apt/sources.list) refer either to
“wheezy” or to “stable”. There should not be
any sources entries pointing to squeeze.

Note

Source lines for a CD-ROM might sometimes refer to
“unstable”; although this may be confusing, you
should not change it.

4.4.1. Recording the session

It is strongly recommended that you use the /usr/bin/script
program to record a transcript of the upgrade session. Then if a problem
occurs, you will have a log of what happened, and if needed, can provide exact
information in a bug report. To start the recording, type:

or similar. If you have to rerun the typescript (e.g. if you have to reboot the
system) use different step values to indicate which
step of the upgrade you are logging. Do not put the typescript file in a
temporary directory such as /tmp or
/var/tmp (files in those directories may be deleted during
the upgrade or during any restart).

The typescript will also allow you to review information that has scrolled
off-screen. If you are at the system's console, just switch to VT2 (using
Alt+F2)
and, after logging in, use
less -R ~root/upgrade-wheezy.script to view
the file.

After you have completed the upgrade, you can stop script by
typing exit at the prompt.

If you have used the -t switch for
script you can use the scriptreplay
program to replay the whole session:

# scriptreplay ~/upgrade-wheezy.time ~/upgrade-wheezy.script

4.4.2. Updating the package list

First the list of available packages for the new release needs to be fetched.
This is done by executing:

# apt-get update

4.4.3. Make sure you have sufficient space for the upgrade

You have to make sure before upgrading your system that you will have sufficient
hard disk space when you start the full system upgrade described in Section 4.4.5, “Upgrading the system”. First, any package needed for installation that
is fetched from the network is stored in
/var/cache/apt/archives (and the
partial/ subdirectory, during download), so you must make
sure you have enough space on the file system partition that holds
/var/ to temporarily download the packages that will be
installed in your system. After the download, you will probably need more
space in other file system partitions in order to both install upgraded
packages (which might contain bigger binaries or more data) and new packages
that will be pulled in for the upgrade. If your system does not have
sufficient space you might end up with an incomplete upgrade that is
difficult to recover from.

apt-get can show you detailed information about the disk
space needed for the installation. Before executing the upgrade, you can see
this estimate by running:

Running this command at the beginning of the upgrade process
may give an error, for the reasons described in the next sections. In that
case you will need to wait until you've done the minimal system upgrade as in
Section 4.4.4, “Minimal system upgrade” before running this command to estimate the
disk space.

If you do not have enough space for the upgrade, apt-get
will warn you with a message like this:

E: You don't have enough free space in /var/cache/apt/archives/.

In this situation, make sure you free up space
beforehand. You can:

Remove packages that have been previously downloaded for installation (at
/var/cache/apt/archives). Cleaning up the package cache by
running apt-get clean will remove all previously downloaded
package files.

Remove forgotten packages. If you have
used aptitude or apt-get to manually
install packages in squeeze it will have kept track of those packages
you manually installed, and will be able to mark as redundant those packages
pulled in by dependencies alone which are no longer needed due to a package
being removed. They will not mark for removal packages that you manually
installed. To remove automatically installed packages that are no longer used,
run:

# apt-get autoremove

You can also use deborphan, debfoster, or
cruft to find redundant packages.
Do not blindly remove the packages these tools present,
especially if you are using aggressive non-default options that are prone to
false positives. It is highly recommended that you manually review the
packages suggested for removal (i.e. their contents, sizes, and descriptions)
before you remove them.

Remove packages that take up too much space and are not currently
needed (you can always reinstall them after the upgrade). If you have
popularity-contest installed, you can use
popcon-largest-unused to list the packages you do not use
that occupy the most space. You can find the packages that just
take up the most disk space with dpigs (available in the
debian-goodies package) or with
wajig (running wajig size).
They can also be found with
aptitude. Start
aptitude in “visual mode”,
select Views → New Flat Package
List, press l and enter
~i, then press S and enter
~installsize. This will give you a handy list to work
with.

Remove translations and localization files from the system if they
are not needed. You can install the localepurge package and configure it so
that only a few selected locales are kept in the system. This will
reduce the disk space consumed at
/usr/share/locale.

Temporarily move to another system, or permanently remove, system logs
residing under /var/log/.

Use a temporary /var/cache/apt/archives: You
can use a temporary cache directory from another filesystem
(USB storage device, temporary hard disk,
filesystem already in use, ...)

Note

Do not use an NFS mount as the network
connection could be interrupted during the upgrade.

For example, if you have a USB drive mounted on /media/usbkey:

remove the packages that have been previously downloaded for
installation:

# apt-get clean

copy the directory
/var/cache/apt/archives to the
USB drive:

# cp -ax /var/cache/apt/archives /media/usbkey/

mount the temporary cache directory on the current one:

# mount --bind /media/usbkey/archives /var/cache/apt/archives

after the upgrade, restore the original
/var/cache/apt/archives directory:

# umount /media/usbkey/archives

remove the remaining /media/usbkey/archives.

You can create the temporary cache directory on whatever filesystem
is mounted on your system.

Do a minimal upgrade of the system (see Section 4.4.4, “Minimal system upgrade”)
or partial upgrades of the system followed by a full upgrade.
This will make it possible to upgrade the system partially, and
allow you to clean the package cache before the full upgrade.

4.4.4. Minimal system upgrade

In some cases, doing the full upgrade (as described below) directly might
remove large numbers of packages that you will want to keep. We therefore
recommend a two-part upgrade process: first a minimal upgrade to overcome these
conflicts, then a full upgrade as described in Section 4.4.5, “Upgrading the system”.

To do this, first run:

# apt-get upgrade

This has the effect of upgrading those packages which can be upgraded without
requiring any other packages to be removed or installed.

The minimal system upgrade can also be useful when the system is tight on space
and a full upgrade cannot be run due to space constraints.

If the apt-listchanges package is
installed, it will (in its default configuration) show important information
about upgraded packages in a pager. Press q after reading
to exit the pager and continue the upgrade.

4.4.5. Upgrading the system

Once you have taken the previous steps, you are now ready to continue
with the main part of the upgrade. Execute:

# apt-get dist-upgrade

Note

The upgrade process for some previous releases recommended the
use of aptitude for the upgrade. This
tool is not recommended for upgrades from squeeze to
wheezy.

This will perform a complete upgrade of the system, installing the newest
available versions of all packages, and resolving all possible dependency changes
between packages in different releases. If necessary, it will install some new
packages (usually new library versions, or renamed packages), and remove any
conflicting obsoleted packages.

When upgrading from a set of CD-ROMs (or DVDs), you will be asked to insert specific CDs
at several points during the upgrade. You might have to insert the same CD
multiple times; this is due to inter-related packages that have been spread out
over the CDs.

New versions of currently installed packages that cannot be upgraded without
changing the install status of another package will be left at their current
version (displayed as “held back”). This can be resolved by either using
aptitude to choose these packages for installation or by
trying apt-get -f install
package.

4.5. Possible issues during upgrade

The following sections describe known issues that might appear
during an upgrade to wheezy.

In some cases the apt-get dist-upgrade step can fail after
downloading packages with:

E: Could not perform immediate configuration on 'package'. Please see man 5 apt.conf under APT::Immediate-Configure for details.

If that happens, running apt-get dist-upgrade -o
APT::Immediate-Configure=0 instead should allow the upgrade
to proceed.

Another possible workaround for this problem is to temporarily add both
squeeze and wheezy sources to your
sources.list and run apt-get update.

4.5.2. Expected removals

The upgrade process to wheezy might ask for the removal of
packages on the system. The precise list of packages will vary depending on the
set of packages that you have installed. These release notes give general
advice on these removals, but if in doubt, it is recommended that you examine
the package removals proposed by each method before proceeding.

4.5.3. Conflicts or Pre-Depends loops

Sometimes it's necessary to enable the APT::Force-LoopBreak
option in APT to be able to temporarily remove an essential package due to a
Conflicts/Pre-Depends loop. apt-get will alert you of this
and abort the upgrade. You can work around this by specifying the option -o
APT::Force-LoopBreak=1 on the apt-get command
line.

It is possible that a system's dependency structure can be so corrupt as to
require manual intervention. Usually this means using
apt-get or

# dpkg --remove package_name

to eliminate some of the offending packages, or

# apt-get -f install
# dpkg --configure --pending

In extreme cases you might have to force re-installation with a command like

# dpkg --install /path/to/package_name.deb

4.5.4. File conflicts

File conflicts should not occur if you upgrade from a “pure” squeeze system, but
can occur if you have unofficial backports installed. A file conflict will
result in an error like:

You can try to solve a file conflict by forcibly removing the package mentioned
on the last line of the error message:

# dpkg -r --force-depends package_name

After fixing things up, you should be able to resume the upgrade by repeating
the previously described apt-get commands.

4.5.5. Configuration changes

During the upgrade, you will be asked questions regarding the configuration
or re-configuration of several packages. When you are asked if any file in
the /etc/init.d directory, or the
/etc/manpath.config file should be replaced by the
package maintainer's version, it's usually necessary to answer “yes” to
ensure system consistency. You can always revert to the old versions, since
they will be saved with a .dpkg-old extension.

If you're not sure what to do, write down the name of the package or file and
sort things out at a later time. You can search in the typescript file to
review the information that was on the screen during the upgrade.

4.5.6. Change of session to console

If you are running the upgrade using the system's local console you
might find that at some points during the upgrade the console is shifted over
to a different view and you lose visibility of the upgrade
process. For example, this may happen in desktop systems when
the display manager is restarted.

To recover the console where the upgrade was running you will have to use
Ctrl+Alt+F1
(if in the graphical startup screen) or
Alt+F1
(if in the local text-mode console) to switch back to the virtual terminal 1.
Replace F1 with the function key with the
same number as the virtual terminal the upgrade was running in. You can also
use Alt+Left Arrow or
Alt+Right
Arrow to switch between the different text-mode terminals.

4.5.7. Special care for specific packages

In most cases, packages should upgrade smoothly between squeeze
and wheezy. There are a small number of cases where some intervention
may be required, either before or during the upgrade; these are detailed
below on a per-package basis.

4.5.7.1. Sudo

If you have modified /etc/sudoers then you should be aware
of changes made to how sudo
configuration is handled. The default /etc/sudoers now
includes the following two directives:

Neither of these entries are added to your /etc/sudoers
automatically during the upgrade. (Although you will still be able to run
sudo commands by specifying their fully-qualified path.) So
you might wish to consider migrating your changes to the new
/etc/sudoers.d directory and using the default
/etc/sudoers file. For example:

You may also need to edit your /etc/sudoers.d/mychanges to
remove unwanted Defaults and #includedir
entries. You should use visudo for this:

# visudo -f /etc/sudoers.d/mychanges

4.5.7.2. Screen

The GNU Screen versions in squeeze and wheezy don't use the same
communication protocol between the screen client
and the SCREEN server. Wheezy's screen package has been patched so that
the most important functionality is present even if the versions of
screen client and server don't match.

The most prominent functionality which does not work properly when
connecting to a Screen session started with squeeze's version of
screen with wheezy's version
of screen as client is
terminal resizing (WINCH signal). The workaround is
to detach and reattach again to get the size of the terminals inside
the screen session adjusted properly.

Some ncurses-based applications, e.g. aptitude in
visual mode, may leave traces of previous contents on the screen.
Pressing
Ctrl+L
solves the issue.

Another (harmless) symptom of such an inter-version connection is
screen issuing messages like "Message 40 of 12376
bytes too small".

All these issues vanish as soon as the Screen sessions started with
squeeze's version of screen
are exited.

See also /usr/share/doc/screen/NEWS.Debian.gz in
wheezy's screen package.

4.5.7.3. Suhosin PHP module

The php5-suhosin package has been
removed. If your PHP configuration included the suhosin module, it will
fail to load after the PHP upgrade. Run dpkg --purge
php5-suhosin to remove the leftover configuration in
/etc/php5/conf.d/suhosin.ini.

4.6. Upgrading your kernel and related packages

This section explains how to upgrade your kernel and identifies potential
issues related to this upgrade. You can either install one of the linux-image-* packages provided by Debian, or
compile a customized kernel from source.

Note that a lot of information in this section is based on the assumption that
you will be using one of the modular Debian kernels, together with initramfs-tools and udev. If you choose to use a custom kernel that
does not require an initrd or if you use a different initrd generator, some of
the information may not be relevant for you.

4.6.1. Installing the kernel metapackage

When you dist-upgrade from squeeze to wheezy, it is strongly
recommended that you install a linux-image-* metapackage, if you haven't done
so before. This package may be installed automatically by the dist-upgrade
process. You can verify this by running:

# dpkg -l "linux-image*" | grep ^ii

If you do not see any output, then you will need to install a new linux-image
package by hand. To see a list of available linux-image metapackages, run:

# apt-cache search linux-image- | grep -v transition

If you are unsure about which package to select, run uname
-r and look for a package with a similar name. For example, if you
see '2.6.32-5-amd64', it is recommended that you install
linux-image-amd64.
You may also use apt-cache to see a long
description of each package in order to help choose the best one
available. For example:

# apt-cache show linux-image-amd64

You should then use apt-get install to install it. Once
this new kernel is installed you should reboot at the next available
opportunity to get the benefits provided by the new kernel version.

For the more adventurous there is an easy way to compile your own custom
kernel on Debian. Install the kernel sources, provided in the linux-source package. You can make use of the
deb-pkg target available in the sources' makefile for
building a binary package. More information can be found in the Debian Linux Kernel
Handbook, which can also be found as the debian-kernel-handbook package.

If possible, it is to your advantage to upgrade the kernel package separately
from the main dist-upgrade to reduce the chances of a
temporarily non-bootable system.
Note that this should only be done after the
minimal upgrade process described in Section 4.4.4, “Minimal system upgrade”.

4.6.2. Boot timing issues (waiting for root device)

If an initrd created with initramfs-tools is used to boot the system, in some
cases the creation of device files by udev can happen too late for the boot scripts to
act on.

The usual symptoms are that the boot will fail because the root file system
cannot be mounted and you are dropped into a debug shell:

Gave up waiting for root device. Common problems:
- Boot args (cat /proc/cmdline)
- Check rootdelay= (did the system wait long enough?)
- Check root= (did the system wait for the right device?)
- Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/something does not exist. Dropping to a shell!
(initramfs)

But if you check afterwards, all devices that are needed are present in
/dev. This has been observed in cases where the root file
system is on a USB disk or on RAID, especially if LILO is used.

A workaround for this issue is to use the boot parameter
rootdelay=9. The value for the
timeout (in seconds) may need to be adjusted.

4.7. Preparing for the next release

After the upgrade there are several things you can do to prepare for the next
release.

4.8. Obsolete packages

Introducing several thousand new packages, wheezy also retires and omits more
than four thousand old packages that were in squeeze. It provides no upgrade path
for these obsolete packages. While nothing prevents you from continuing to use
an obsolete package where desired, the Debian project will usually discontinue
security support for it a year after wheezy's release[5], and will
not normally provide other support in the meantime. Replacing them with
available alternatives, if any, is recommended.

There are many reasons why packages might have been removed from the
distribution: they are no longer maintained upstream; there is no longer a
Debian Developer interested in maintaining the packages; the functionality they
provide has been superseded by different software (or a new version); or they
are no longer considered suitable for wheezy due to bugs in them. In the latter
case, packages might still be present in the “unstable” distribution.

Detecting which packages in an updated system are “obsolete” is easy since the
package management front-ends will mark them as such. If you are using
aptitude, you will see a listing of these packages in the
“Obsolete and Locally Created Packages” entry.

postgresql-8.4, successor is
postgresql-9.1.
Wheezy provides only an updated
postgresql-plperl-8.4 package
that is linked against the new version of libperl in order to enable
upgrading to the new Perl version in wheezy without making existing
postgresql-8.4 installations unusable. Once the operating system
upgrade is finished, you should plan to also upgrade your PostgreSQL
8.4 database clusters to the new PostgreSQL version 9.1 using the
pg_upgradecluster tool.

python2.5, successor is
python2.7.

portmap, successor is
rpcbind.

sun-java6, successor is
openjdk-7.

gdm, successor is
gdm3. Users of lightweight
desktop environments such as Xfce or LXDE may wish to consider
lightdm as a lighter
weight alternative.

Some of Xorg's video drivers are no longer available in
wheezy and are obsolete. This includes
xserver-xorg-video-nv and
xserver-xorg-video-radeonhd.
They may be removed during the upgrade. Users should install
xserver-xorg-video-all
instead.

All Horde 3 packages, providing web collaborative software, have been
removed and are obsolete. This includes
ansel1,
chora2,
dimp1,
gollem,
horde-sam,
horde3,
imp4,
ingo1,
kronolith2,
mnemo2,
nag2,
sork-forwards-h3,
sork-passwd-h3,
sork-vacation-h3 and
turba2.
As the Horde 4 packages have not reached sufficient quality before the
wheezy release, they are also not available. They may be available
in testing as
php-horde-* packages.

Most Kolab packages, providing groupware server, have been removed. This
includes
kolab-cyrus-imapd,
kolab-webadmin,
kolabd,
libkolab-perl,
php-kolab-filter and
php-kolab-freebusy.
As of 2012, Kolab was in a major rewrite and may get shipped with a
later Debian release as the
kolab package. NB: The SOGo
server (formerly named Scalable OpenGroupware.org) is shipped with
wheezy as sogo.

All OpenERP 5 packages have been
removed and are obsolete. This includes
openerp-client,
openerp-server,
openerp-web.

The pootle 2.0.5
package has been removed.

The uw-imapd and ipopd packages have been removed. Better
alternatives exist, for example dovecot-imapd and courier-imap for IMAP, or dovecot-pop3d and courier-pop for POP3.

The drupal6 package is no
longer available; it is replaced by drupal7. However, no automatic upgrade
path exists, and users should read the instructions on the Debian Wiki.

4.8.1. Dummy packages

Some packages from squeeze have been split into several packages in wheezy, often
to improve system maintainability. To ease the upgrade path in such cases,
wheezy often provides “dummy” packages: empty packages that have the same name as
the old package in squeeze with dependencies that cause the new packages to be
installed. These “dummy” packages are considered redundant after the
upgrade and can be safely removed.

Most (but not all) dummy packages' descriptions indicate their purpose.
Package descriptions for dummy packages are not uniform, however, so you might
also find deborphan with the
--guess-* options (e.g.
--guess-dummy) useful to detect them in your system. Note
that some dummy packages are not intended to be removed after an upgrade but
are, instead, used to keep track of the current available version of a program
over time.

[1] If the debconf
priority is set to a very high level you might prevent configuration prompts,
but services that rely on default answers that are not applicable to your
system will fail to start.

[2] For example: DNS or DHCP services, especially when
there is no redundancy or failover. In the DHCP case end-users might be disconnected
from the network if the lease time is lower than the time it takes for the
upgrade process to complete.

[3] This feature can be disabled by adding the parameter
panic=0 to your boot parameters.

[4] Debian's package management system normally
does not allow a package to remove or replace a file owned by another package
unless it has been defined to replace that package.

[5] Or for as
long as there is not another release in that time frame. Typically only two
stable releases are supported at any given time.